Vehicle and sealing glass paste and method for making same

Abstract

Sealing glass paste for sealing the face plate and funnel portion of a color television tube wherein PbO-containing sealing glass frit contains from at least 0.1 to 1.5% by weight of Pb 3 O 4 powder, which powder prevents the reduction of PbO to Pb metal during the sealing process, which reduction would otherwise result in a dielectric breakdown in the seal. A sealing glass paste consisting essentially of a PbO--B 2 O 3 --ZnO sealing glass frit and containing from at least 0.1 to 1.5% by weight of Pb 3 O 4 powder, based upon the weight of the frit, together with hydroxypropyl cellulose binder for the frit and a solvent for the binder. A method for sealing the face plate of a color television tube to its funnel portion with a PbO-containing solder glass wherein the reduction of PbO to metallic lead during the sealing step is obviated by the addition of a sufficient amount of Pb 3 O 4 powder in the solder glass and paste made therewith, which Pb 3 O 4 is slowly reduced to PbO in a reducing atmosphere during the sealing of the television tube components. A method for increasing the dielectric properties of a PbO-containing sealing glass paste and the devitrified seal made therefrom, which seals the face plate to the funnel of a color television tube, to a value greater than that provided by the solder glass, per se, by incorporating in the solder glass and the solder glass paste made therefrom a small but sufficient amount of Pb 3 O 4 to accomplish this purpose. A vehicle for a glass frit comprises hydroxypropyl cellulose as a binder and a solvent for said binder.

We claim: 
     
       1. A vehicle for a glass frit, said vehicle comprising a solution of: A. nitrocellulose   B. a solvent selected from the group consisting of amyl acetate, methyl amyl acetate, ethyl hexyl acetate, n-butyl acetate, isobutyl acetate, sec. butyl acetate and diethylene glycol monobutyl ether acetates;   C. hydroxypropyl cellulose having a molecular weight of about 40,000 to about 300,000; and   D. a solvent selected from the group consisting of ethylene glycol methyl ether and ethylene glycol ethyl ether; wherein said hydroxypropyl cellulose is present in an amount sufficient to impart stability to a paste comprising said vehicle and frit.   
     
     
       2. Vehicle according to claim 1 which comprises in weight percent:   hydroxypropyl cellulose                                                   
                      0.195   -      1.2                                  
nitrocellulose        0.84    -      5.9                                  
amyl acetate         83.5     -     96.45                                 
ethylene glycol methyl ether                                              
                      2.4     -     14.4.                                 
     
     
     
       3. Vehicle according to claim 2 in which said hydroxypropyl cellulose has an average molecular weight of about 60,000. 
     
     
       4. Vehicle according to claim 1, wherein said solvent comprises amyl acetate in admixture with ethylene glycol methyl ether. 
     
     
       5. Vehicle according to claim 1 which comprises about 5 to 30% by weight of a 4-weight percent solution of hydroxypropyl cellulose in equal parts by weight of amyl acetate and ethylene glycol methyl ether, and about 95 to 70% by weight of a 1 to 6.2 weight percent solution of nitrocellulose in amyl acetate. 
     
     
       6. Vehicle according to claim 1 which comprises in weight percent:   hydroxypropyl cellulose  0.2                                              
nitrocellulose           1.1                                              
amyl acetate             96.3                                             
ethylene glycol methyl ether                                              
                          2.4.